Fluoroolefins represented by formula: CF3(CX2)nCF═CH2, formula: CF3(CX2)nCH═CHF, and the like are compounds having a useful structure as various functional materials, solvents, refrigerants, blowing agents, and the monomers for functional polymers or the starting materials of such monomers. Fluoroolefins are used, for example, as monomers for modifying an ethylene-tetrafluoroethylene copolymer. Of these fluoroolefins, the compound represented by CF3CH═CH3 (HFO-1234yf) and the compound represented by CF3CH═CHF (HFO-1234ze) have recently gained attention, as they offer promising prospects as refrigerants with low global warming potential.
As an example of methods for producing the fluoroolefins represented by the formulae above, a method has been reported in which a chlorine-containing alkane or chlorine containing alkene starting material having the same number of carbon atoms as that of a target fluoroolefin is reacted with a fluorinating agent, such as an anhydrous hydrogen fluoride, in the presence of a catalyst (see Patent Literature (PTL) 1 below).
In particular, HFO-1234yf, which is gathering attention as a refrigerant with low global warming potential, is produced by a gas-phase continuous fluorination reaction of chlorine-containing olefins, such as HCFO-1233xf, in the presence of a catalyst. A method is also known that additionally uses a gas having oxidizing properties, such as oxygen and chlorine, to prevent catalyst deterioration caused by a long-term continuous reaction.
However, the use of oxygen gas to prevent catalyst deterioration requires a reaction temperature of about 350° C. or higher. If the reaction is performed at a temperature of about 350° C. or lower so as to maintain optimum selectivity or optimum catalyst stability, it is impossible to sufficiently obtain an effect of suppressing catalyst deterioration. Furthermore, to sufficiently obtain an effect of suppressing catalyst deterioration, a relatively large amount of oxygen is required.
The addition of chlorine gas to prevent catalyst deterioration poses a problem in that chlorine gas, which has a high reactivity, acts on the starting material or product, and reduces the selectivity of the target product. In particular, the thermal addition of chlorine gas easily occurs with respect, to a double-bond-containing starting material or product, which results in a great reduction in the selectivity of the target product.
Moreover, in any case, when a gas for preventing deterioration is once added, it stays with the fluoroolefin until the end of the production process, causing a problem at the time of purification in that the gas serves as a non-condensable gas and inhibits the separation and purification of fluoroolefin.